The present invention relates to a zooming lens barrel for a photographing apparatus such as cameras, or the like, and more specifically to a zooming lens barrel having a view finder lens in which magnification is changed by zooming.
Recently, cameras with a lens shutter (a lens shutter camera, on which a zooming lens is mounted, have been popular, and normally, its view finder is an external-light type zoom finder. A zooming finder is mechanically interlocked with the zooming operation of a photographic lens.
In a zooming lens, the focal distance, that is, the photographic magnification is changed. Competition is keen for techniques for an increase of a variable magnification ratio, which is a ratio of the longest focal distance to the shortest focal distance, and for downsizing the zooming lens barrel. The technique for increasing the variable magnification ratio and that for downsizing the lens barrel are reciprocal to each other. Recently, however, various types of zooming lens barrels, in which dimensions of the lens barrel are not increased even in the case of the high variable magnification ratio, have been proposed.
As an example, a zooming lens barrel has been disclosed by the present applicant in Japanese Patent Publication Open to Public Inspection No. 226562/1994. That is, in this zooming lens barrel, focusing distance switching operations and focusing are conducted by a moving means such as a single motor or cams, and the structure for selecting the focusing distance switching operations and focusing in discrete steps is described in this patent publication.
In conventional zooming lenses, the change of the focal distance, i.e. zooming, and the focal point adjustment, i.e. focusing, are respectively conducted by independent mechanisms. However, in this patent publication, zooming and focusing can be conducted by the same mechanism, resulting in the realization of a very small size zooming lens barrel.
In this patent publication, this is a type of a zooming lens, in which the distance between the longest focal distance and the shortest focal distance is divided into a predetermined number of steps, that is, a so-called stepped zooming type lens. This step zooming method is explained in a zooming diagram shown in FIG. 1. In this diagram, the horizontal axis expresses the change of focal distance. In FIG. 1, W shows the shortest focal distance, the focal distance successively increases at M.sub.1 and M.sub.2, and T shows the longest focal distance. In this way, the focal distance is switched at 4 steps. The vertical axis shows the movement amount of the front lens component and the rear lens component of the photographic lens in the direction of the optical axis.
The front lens component is helicoidally screwed into a rotatable cam cylinder, and accordingly, the front lens component is linearly moved by the rotation of a lens frame. On the other hand, the rear lens component is driven by a cam formed on the cam cylinder. With regard to the photographic distance U, the cam is formed such that the rear lens component moves on a saw-toothed curve between .infin., i.e. the infinity focusing position and N, i.e. the nearest focusing position, as illustrated in FIG. 1. In the case where focusing is conducted when the focal distance is set at a position W, the front lens component and the rear lens component move between W and 1 corresponding to the photographic distance. When zooming is conducted toward the telephoto side by 1 step, the front lens component and the rear lens component move to a position M.sub.1 through 1. In the same way, when zooming is conducted by 2 steps toward the telephoto side, the front lens component and the rear lens component move to a position M.sub.2 through 1, M.sub.1, 2. Since the zooming lens is structured such that focusing and zooming are continuously conducted repeatedly by movement of the front lens component and the rear lens component, the front lens component and the rear lens component can be driven by the same mechanism as that for focusing and for zooming, so that the number of parts is inevitably decreased and the structure is simpler, resulting in a smaller sized zooming lens barrel.
The invention in the patent publication as explained above, much contributes to downsizing the zooming lens barrel; and the camera, to which this invention has been applied, is now being manufactured. However, the lens mounted on this camera is a zooming lens, the variable magnification ratio of which is 2. In the case where the zooming lens with a higher magnification ratio is mounted on the camera, the abovedescribed invention does not necessarily apply.
That is, when a zooming lens with a higher magnification ratio is used, it is necessary that a larger number of steps are adopted in the zooming lens, to utilize its advantage of high magnification. An enlarged view of the zooming diagram in FIG. 1 is shown in FIG. 2. In the same way as described above, when focusing is conducted at a focal distance position M.sub.W, the rear lens component moves between 1 and 2, as shown in FIG. 2. Next, when zooming is conducted toward the telephoto side by 1 step, the rear lens component moves to 3 through 2, and is located at a focal distance position M.sub.T. In this zooming diagram, in the case where the number of steps are increased by using a zooming lens with a high magnification ratio, M.sub.M is positioned in the middle of M.sub.T and M.sub.W, and zooming is conducted by 1 step, then, the rear lens component moves to 4 through 2, and is located at the focal distance M.sub.M. Then, as can clearly be seen from FIG. 2, when the slope .theta..sub.1 of the line between 2 and 3, is compared to the slope .theta..sub.2 of the line between 2 and 4, the slope .theta..sub.2 is larger than the slope .theta..sub.1. Accordingly, the mechanical load to move the rear lens component is increased, and there is a possibility that the rear lens component can not be moved depending on the slope.
Accordingly, in order to decrease the slope .theta..sub.2 and to easily operate the rear lens component, it is necessary to enlarge the step interval. However, the enlargement of the step interval in the direction of the horizontal axis, causes enlargement of the circumferential length of the cam cylinder, that is, enlargement of the diameter of the cam cylinder, resulting in a bigger lens barrel.
In order to solve the above problems, the present applicant proposed the following invention.
FIG. 3 is a zooming diagram showing the focal distance divided into 8 steps. In FIG. 3, the horizontal axis shows changes of the focal distance. The vertical axis shows movement of the front lens component and the rear lens component of the photographic lens in the direction of the optical axis. The front lens component is linearly moved by the helicoidal drive. The rear lens component moves in the direction which is separated from the front lens component and in the direction which approaches the front lens component, and this movement is reciprocally repeated. For example, in the case where the focal distance position is W, when zooming is conducted toward the telephoto side by 1 step, the focal distance position changes from W to M.sub.1. Further, when zooming is conducted by 1 step, the focal distance position changes from M.sub.1 to M.sub.2. As described above, zooming can be conducted in 8 steps between W and T.
On the other hand, for example, when the focal distance position is W, focusing is conducted such that the front lens component and the rear lens component are moved from the focusing position on the infinity (.infin.) side to that on the nearest (N) side in order to focus between W and M.sub.1. Further, when the focal distance position is M.sub.1, the front lens component and the rear lens component are moved from the focusing position on the nearest (N) side to that on the infinity (.infin.) side in order to focus between M.sub.1 and M.sub.2. As described above, focusing is conducted at all steps prepared in the zooming area between W and T. This zooming lens is structured such that the rear lens component moves repeatedly from the infinity position to the nearest distance position, and from the nearest distance position to the infinity position, while the front lens component moves linearly.
Accordingly, in this zooming diagram, the focusing area is continuously provided in the zooming area. Accordingly, when this diagram is compared with that of the conventional technique in FIG. 1, although the number of steps of the focal distance position is 4 in FIG. 1, that in this diagram is increased to 8, which is two times the conventional one. However, in this diagram, the slope for the movement of the rear lens component is not increased, and the rear lens component can be smoothly operated.
That is, in the conventional technique, when focusing is conducted at an arbitrary focus position, the zooming lens always moves from the focusing position on the nearest distance side toward the focusing position on the infinity side, or from the focusing position on the infinity side toward the focusing position on the nearest side. However, in the zooming lens barrel described above, when focusing is conducted at an arbitrary position, the zooming lens moves from the focusing position on the nearest distance side toward the focusing position on the infinity side, and is switched to the next focus position. At this focus position, focusing is conducted when the zooming lens moves the focusing position on the infinity side toward the focusing position on the nearest side, the number of zooming steps (focus positions) can be increased.
FIG. 4 is a zooming diagram in which a zooming lens, having the same maximum focal distance as that in FIG. 1, moves in four steps. In FIG. 4, since the zooming lens is structured in the same way as that in FIG. 3, the slope, on which the rear lens component moves, is decreased more than that in FIG. 1, and the cam cylinder can move more smoothly.
A zooming view finder is driven, being interlocked with the zooming lens barrel, as described above. A magnification ratio of the zooming view finder is changed, being interlocked with that of the zooming lens. Further, it is ideal that the frame of a visual field moves being interlocked with the photographic distance, and a parallax is compensated for. However, because automatic focusing cameras are now commonly used, the photographic lens is not driven even when distance measuring is conducted by pressing a release button in one step while a photographer is viewing through the view finder at the time of photography, and the view finder is not interlocked with the photographic distance. Actually, when the release button is pressed in step 2, the photographic lens is moved. At this time, the shutter is immediately opened and closed. Accordingly, there is no meaning even when the view finder is interlocked with the movement of the photographic lens at this time. Therefore, it is required to select the focal distance position, and to move the view finder to a predetermined position and to stop it there.
On the other hand, the most frequently used photographic distance is in the range between infinity and 1.5 m, and in the case of the visual field of the view finder for the distance smaller than 1.5 m, a short distance correction mark, which is separately provided on the view finder, is used. Accordingly, when the visual field of the view finder is set at approximately 3 m, which is an intermediate distance, there is practically no problem in the fixed frame of the visual field in the range from infinity to 1.5 m. Therefore, the frame of the visual field of the view finder in the above invention is set to 3 m at each focal distance.
FIG. 5 is a partially enlarged view showing the movement of the rear lens component in the zooming diagram in FIG. 3. The horizontal axis shows the focal distance, and the vertical axis shows the amount of movement of the rear lens component. In the upper left portion of the drawing, the magnification M of the zooming view finder, which is interlocked with the zooming lens, is shown. In the drawing, when the focal distance position is set to 40 mm, the rear lens component is located at the position L.sub.1, and moves between L.sub.1 at 1.5 m and L.sub.2 at .infin. when focusing. Before the release button is pressed, the view finder is set at the position f.sub.1 of 3 m, which is an intermediate position between 1.5 m and .infin.. In the same way, when the focal distance position is set to 45 mm, the rear lens component is located at the position of L.sub.2, and moves between L.sub.2 at .infin. and L.sub.3 at 1.5 m when focusing. The view finder is set for 3 m at the position f.sub.2, which is an intermediate value between .infin. and 1.5 m. In the same way, hereinafter, the view finder is set to the position f.sub.3, at the focal distance of 50 mm, and to the position f.sub.4 at the focal distance of 55 mm. Here, f.sub.1 is intermediate between L.sub.1 and L.sub.2, f.sub.2 is intermediate between L.sub.2 and L.sub.3, and f.sub.3 and f.sub.4 are also set in the same way as described above. Accordingly, because the distance between f.sub.1 and f.sub.2, and that between f.sub.2 and f.sub.3, and between f.sub.3 and f.sub.4 are equal or almost equal, the magnification of an image, formed by the view finder, is changed at a constant ratio when the focal distance position is changed. When the photographer conducts zooming while viewing through the view finder, there is no strange feeling for photographing.
FIG. 6 is an enlarged view of the zooming diagram expressed in the same way as in FIG. 5. In FIG. 6, the nearest distance is set at 0.8 m so that close-up photography can be conducted. However, as described above, it is necessary to set the view finder at almost 1.6 m which is an intermediate value between .infin. and 0.8 m so that the magnification of the view finder is changed at a constant ratio. Further, because the focal distance changes during focusing, the difference between the visual field, confirmed by the view finder set at 1.6 m, and the actual picture area becomes larger when photographed at .infin. or 0.8 m. That is, when photographed at the infinity side of the zooming lens, the actual picture area is larger than the area confirmed by the view finder, so that the image becomes smaller. Reversely, when photographed at the nearest distance side, the actual picture area is smaller than the apparent area indicated by the view finder, so that the image becomes larger. That is, an influence due to change of the visual field tends to occur, which is a problem.
FIG. 7 is a zooming diagram expressed in the same way as those described above. In FIG. 7, the nearest distance is set at 0.8 m, and the visual field of the view finder, which is an area confirmed by the view finder, is set at 3 m. In this case, the difference between the visual field of the view finder set at 3 m and an actual picture area at the photographic distance of .infin. is not problem. However, as described above, at the distance of 0.8, since there is a problem in which the difference between the visual field confirmed by the view finder and the actual picture area becomes larger, it is necessary to provide a close-up compensation mark in the view finder. However, as can easily be seen from the drawing, although the interval between f.sub.1 and f.sub.2 is equal to the interval between f.sub.3 and f.sub.4, the interval between f.sub.1 and f.sub.2 is not equal to that between f.sub.2 and f.sub.3. Accordingly, when the focal distance is changed, the magnification of the view finder becomes not a simple constant gain, but a waving gain. Therefore, when the photographer conducts zooming while viewing through the view finder, a strange feeling for photographing occurs, which is another problem.
Further, in current lens shutter cameras, it is required, as described above, to increase the magnification ratio of the photographing lens, and further to enhance the speed of the photographing motions so as not to lose the photo opportunity. Therefore, it is intended to enhance the speed of photography such that each operation provided in the camera, for example, a zooming operation, a focusing operation, etc., is conducted in the shortest period of time possible. Specifically, it is required to conduct the focusing operation, which greatly contributes to reduction of the photographic time itself, at a higher speed, which is a further problem.